1. Field of the Invention
The present invention relates to a post-processing apparatus and an image forming system, and more particularly to a post-processing apparatus configured to collect printed sheets ejected from an image forming apparatus and to handle the printed sheets, and an image forming system comprising the post-processing apparatus.
2. Description of Related Art
As a post-processing apparatus for collecting and handling printed sheets ejected from an image forming apparatus, for example, a sheet post-processing apparatus disclosed by Japanese Patent Laid-Open Publication No. 2005-314029 is known. Such a conventional sheet post-processing apparatus is described with reference to FIGS. 14 and 15.
As shown by FIG. 14, the sheet post-processing apparatus 500B is to handle, for example, fold and/or staple sheets P ejected from an image forming apparatus 500A, and the sheet post-processing apparatus 500B is connected to the image forming apparatus 500A. The sheet post-processing apparatus 500B comprises a sheet feeding unit 600, and the sheet feeding unit 600 comprises an intermediate stacker 700.
As shown by FIG. 15, the intermediate stacker 700 comprises guide plates 562A and 562B, a sheet stopper 563, and a friction member 565. The guide plates 562A and 562B are opposed to each other and are arranged vertically. At the bottom of the guide plates 562A and 562B, the sheet stopper 563 and the friction member 565 are located. The sheet stopper 563 is movable to adjust its position to the sheet size.
The intermediate stacker 700 of the structure above temporarily stores therein the sheets P to be handled, for example, to be folded and/or stapled. Specifically, each sheet P introduced into the sheet post-processing apparatus 500B through an entrance 510 passes through entrance rollers 511, feed rollers 517 and a sheet path r502 and enters an area between the guide plates 562A and 562B. Then, the sheet P slides down along the guide plates 562A and 562B and is stopped by the sheet stopper 563. In this way, sheets P are collected and stored in the intermediate stacker 700.
At this stage, if the sheet P slides down too fast, the stopper 563 may be pushed down by the impact of a collision of the sheet P with the stopper 563. In order to avoid this trouble, in the intermediate stacker 700, the friction member 565 is located immediately above the sheet stopper 563. The sheet P sliding down along the guide plates 562A and 562B comes into contact with the friction member 565 before hitting against the sheet stopper 563. Thereby, the sliding sheet P slows down, and a fall of the stopper 563 due to the collision of the sheet P can be avoided.
In the method of slowing down the sliding sheet P by use of the friction member 565, however, the degree of slowing-down changes depending on the coefficient of friction of the surface of the friction member 565, the size and the grammage of the sheet P, etc. Therefore, the intermediate stacker 700 has a problem that there may be cases in which the sheet P does not reach the stopper 563 when the grammage of the sheet P is small or when the coefficient of friction of the friction member 565 is high.